Abstract Abuse of legal prescription drugs, particularly opioids, is a growing problem in the United States. The abuse leads to addiction, negative health outcomes, increased disability costs, and death caused by overdose or poisoning. Sales of prescription opioids and the negative health outcomes related to opioid use grew rapidly over the past decade. Overdoses, reports of abuse, and enrollment in drug treatment programs for prescription drugs are larger than for illicit drugs. In 2007, opioid overdoses became the second leading cause of unintentional death. Estimates place the total societal costs of this abuse at nearly $56 billion. Recent research has shown that the problem of licit drug abuse extends to the Medicare population where there are many documented cases of fraudulent utilization of opioids. The White House branded this increase in prescription drug abuse a public health and safety crisis. In response, states are experimenting with various solutions to this growing epidemic. Anecdotal evidence has shown positive results for some of these laws, but there is no systematic analysis of the impact of those efforts on opioid use and abuse. A key impediment to a thorough understanding of the impact of these state laws on opioid use and abuse is a lack of sufficiently detailed, representative data on medical and prescription drug claims. By relying on a 20 percent sample of all Medicare inpatient, outpatient, office, and prescription drug claims, alongside detailed demographic information, this project will assess the extent of opioid use and abuse in the Medicare population and the impact of these state laws in affecting that use and abuse. I will also characterize predictors of opioid use and abuse and describe the time trends in opioid use as well as differences in use by age, race/ethnicity, gender, Medicare eligibility status, and income. I will develop novel indicators of opioid abuse based on administrative claims and validated against medical diagnoses. I will create a state- level database on the type and effective dates of state regulations of prescription drugs. Finally, I will exploit the state-level variation in effective dates to empirically estimatethe causal impact of these laws on measures of opioid use and abuse.